Russia has dismissed U.S. accusations that Syrian forces used chemical weapons, calling the charge "utter nonsense," and warned that a military intervention without United Nations authorization would be a violation of international law. But what, if anything, could Russia do to retaliate?

It's a question that's sparked a fair share of handwringing in the past week, given Russia's close alliance with Syrian President Bashar al-Assad. But experts agree there's little evidence to suggest that Russia will do much more than complain loudly and continue to do what it's already been doing in Syria.

"Russian options for 'punishing' the U.S. appear limited," Steven Pifer, a former U.S. Ambassador to Ukraine who is now with the Brookings Institution, told ABC News.

Russia is staunchly opposed to Western intervention in Syria. Moscow is Syria's last major ally, its arms dealer and its financial backer. The alliance provides Russia with its last vestige of influence in the region and a foothold in the Mediterranean. Aside from that, since the dissolution of the Soviet Union, the Kremlin also has a long-held opposition to foreign intervention in domestic conflicts.

What we are likely to see, experts agree, is Russia continuing to block any efforts at the U.N. Security Council to authorize force or even pressure or condemn Assad. They'll complain loudly about U.S. meddling and warn of regional consequences.

But at the end of the day, Russia knows it can't stop the U.S. from intervening, and its response is likely to be muted simply because it's not in Russia's interest to get involved in the conflict, isolate itself further, or stop cooperating on areas in which it has interests.

Pifer said Russian President Vladimir Putin would be wise to play down his displeasure, since making too much noise would "highlight Russia's impotence to stop it."

The Kremlin will likely continue to arm and fund the Assad government, perhaps in increased numbers, but as Reuters reported this week, that arms relationship was already deepening in recent months.

Here's a few things that Russia most likely will NOT do ...

Attack

Foreign Minister Sergei Lavrov said it clearly on Monday: Russia is "not planning to go to war with anyone" over Syria. Those ships headed to the Mediterranean? They've been moving in and out on rotations for a couple of years. They may send a signal, but in the end the most they'll likely do is evacuate Russian citizens if things get worse.

Go all out to support Assad

Russia has been propping up the Assad government, but quietly and at insufficient levels to tip the scales in the government's favor. Throughout the conflict Russia continued to "fulfill existing contracts" for "defensive" weapons like air and coastal defense systems, but it has stopped at shipping the advanced S-300 air defense system, which Syria had already purchased. Putin himself said in June that Russia would not send Assad the S-300 because "we don't want to throw the region off-balance."

"My guess is measured criticism with perhaps some symbolic gesture to Assad -- though even there Moscow needs to be careful so as not to alienate further the Arab world," Pifer said.

Cut ties with the U.S.

U.S.-Russia relations are already on the rocks amid disagreements over missile defense, Russia's decision to grant NSA leaker Edward Snowden asylum, and President Obama's decision to back out of a summit with Putin, but that doesn't mean nothing is happening.

Both sides continue to talk about issues like missile defense and arms control, even if there are no breakthroughs. Observers of Russia have noted that Russia is very good at compartmentalizing issues within the relationship. That is, if things are bad in one area they don't let it affect another area. If something is in their interest they'll pursue it, regardless of what's happening elsewhere. If it's not, they won't waste their time and energy.

In the end, both the U.S. and Russia may decide to make a symbolic gesture when they see each other next week at the G20 summit, which Russia will host in St, Petersburg. Putin suggested today that world powers discuss the Syria situation during the G20.

"My guess is he and Obama will recommit to a Geneva II process as the best face-saving solution," Matt Rojansky, director of the Kennan Institute at the Wilson Center, told ABC News, referring to the long-delayed U.S. and Russian efforts to set up an international peace conference.

Step up cooperation with Iran, or block the U.S. elsewhere like Afghanistan

Again, it's not really in Russia's interest to do so geopolitically, which means they likely won't do it. Russia is already concerned about NATO's pullout in Afghanistan, so they have reasons to continue helping there. Russia has no incentive to start helping Iran either. Just this week, amid all the disagreements over Syria, it was announced that the advanced S-300 air defense system that Russia sold to Iran several years ago and never delivered has already been dismantled and recycled.

The bigger concern for Putin may be looking weak at home, unable to stop the Americans. It all comes just as the world spotlight will shine on Russia when it hosts the G20 summit. But, in the end he may come out on top.

"In the longer term, since the strike is not likely to accomplish anything, and the U.S. won't put troops on the ground, Putin will look better for having opposed it," Rojansky said.